1. Field of the invention
The present invention relates to an electric power supply control system for a vehicle, namely, to be mounted to a vehicle equipped with an alternator and various types of electric power systems.
2. Description of the Related Art
There has been well known an electric power supply control system capable of performing control of the entire vehicle. The electric power supply control system is capable of supplying electric power accumulated in various electric power sources (such as an alternator and a secondary battery) to on-vehicle devices. Those on-vehicle devices are grouped in function. For example, Japanese patent laid open publication number JP 2002-300734 has disclosed such a conventional electric power supply control system.
There has also been well known an electric power source system which is capable of performing the entire control of a vehicle by detecting a load current of each on-vehicle device and supplying the electric power to the on-vehicle devices. The electric power source system also manages the power consumption of those on-vehicle devices. For example, Japanese patent laid open publication number JP 2004-194364 has disclosed such a conventional electric power source system.
The above conventional techniques disclosed in JP 2002-300734 and JP 2004-194364 involve the following drawbacks (1) to (5) when mounting the total electric power supply control system to the vehicle in order to manage the electric power supply to various types of on-vehicle devices.    (1) A large system is required, and it is also expensive to perform the central management for distributing and supplying electric power to various on-vehicle electrical devices. Because there are various combinations of on-vehicle electrical devices according to vehicle types and devices being used, it is necessary to change or modify the structure of the central management system for every variation. Such a change requires the central management system to be re-designed and therefore requires a lot of works.    (2) It is common knowledge for a designer having skill in this art to design an electric management system to be mounted to a vehicle so that an alternator supplies electric power to on-vehicle electrical devices during a normal operation in order to avoid the battery becoming dead due to energy discharge. Accordingly, there is not necessarily a demand to incorporate the central management system into a vehicle.    (3) However, recently, various types of on-vehicle mechanical devices such as power steering, brakes, and a stabilizer are replaced with electrically driven devices such as an electrical power steering, electrical brakes, and electrical stabilizer. Those electrically driven devices do not always operate. In other words, those electrical devices are driven according to the driving condition of the vehicle. Because those on-vehicle electrical devices need a high level of electrical power which is more than the electric power output from the on-vehicle alternator when those electrical devices operate, the on-vehicle battery must temporarily supply an insufficient amount of the electrical power to those electrical devices. Unfortunately, when the battery falls into a low capacitance condition or when the battery almost reaches the end of its useful lifetime and an inner electrical resistance of the battery is increased, it becomes difficult for the battery to keep the necessary output voltage and to supply an adequate amount of electrical energy to those targeted electrical devices. Due to this inadequate supply of electrical energy the on-vehicle electrical devices are rendered inoperative.    (4) Because those conventional central management systems described above are generally equipped with one or more electrical motors, a rush current occurs when the motor initiates its operation. However, the conventional central management systems do not take such a rush current into account.    (5) Further, when damage occurs in a part of the conventional central management system, which is capable of totally managing the electric power supply to various types of electrical loads using a large amount of electric power mounted to a vehicle, the damage affects all of the electrical loads. In this regard, there has been a strong demand to improve or re-design the conventional central management system in consideration of the importance of safety.
When a vehicle adopts a central management system capable of totally managing the on-vehicle electrical devices and when the central management system is enlarged, it is necessary to perform re-designing of the entire central management system. This requires complicated design work. In general, the response characteristic of the central management system becomes bad or low because it is necessary for the central management system to control the operation of the on-vehicle electrical devices (or loads) after a complete inspection of the condition of the system.